The invention relates to a method of increasing the viscosity of a composition containing an oil by the addition of a long chain carboxylic acid. In addition, the invention relates to the resultant composition. In particular, the invention relates to a process of thickening oils, thereby enhancing the viscosity of desired formulations. The invention has particular applicability in the cosmetic and pharmaceutical industries.
A large number of lubricant formulations are used in various technical fields, especially in the cosmetic and pharmaceutical industries. The viscosity of such formulations is increased by using various oil thickening agents. In the cosmetic industry, the resulting products are often referred to as oleogels. In the pharmaceutical industry, such products are often referred to as pharmaceutical adjuvants.
Typically, highly dispersed silica including clays, fumed silicas, castor wax and microcrystalline high-melting fats such as hardened glycerides of relatively long chain length, have been used to increase the viscosity of lubricant formulations. In light of their thickening capabilities, metallic soaps, fatty acid dextrin esters, metallic salts of dialkyl phosphate and organic-denatured bentonites have further been used as thickening agents for medicines and cosmetics. Most particularly, the prior art tended to favor the use of hydrogenated castor oil.
The thickening systems of the prior art were relatively unstable at elevated temperatures. When stored or transported under higher temperature conditions, such systems often decomposed. In addition, such systems often were highly filamentous.
Organic-denatured bentonites have further been used as thickening agents for providing thixotropic rheological characteristics to oils. Organic-denatured bentonites, however, are generally produced through intercalation of an alkyl amine on montmorillonite which is a clay mineral. This poses a problem in view of safety of alkyl amine when the material is used for medicines or cosmetics. Furthermore, the turbidity caused by an organic-denatured bentonite, in light of inclusions of montmorillonite, often affected the color of the resulting composition. For this reason, organic-denatured bentonites are unsuitable in those circumstances where the resultant composition is to have a delicate color tone.
There is, therefore, a strong need for the development of thickening agents having thixotropic and rheologically acceptable characteristics, which exhibit good color while imparting a fresh feel to the users, which does not form filamentous materials and which is heat stable.
The invention relates to a process of preparing a composition of enhanced viscosity and a composition resulting therefrom. The process consists of adding to an oil a monocarboxylic acid having a number average molecular weight of less than 3,000.
The amount of carboxylic acid used in combination with the oil is between from about 1.0 to about 20% by weight.
The resulting composition exhibits good heat stability, is non-filamentous and is a desired feel modifier. Such compositions may be used topically or internally and have particular utility in the production of cosmetics and pharmaceuticals.
The carboxylic acids employed in the invention are preferably a monocarboxylic acid of the formula RCOOH wherein R is a branched or linear saturated hydrocarbon chain of number average molecular weight less than 3,000.